The invention relates to a ball actuator of great efficiency and with small dimensions, designed in particular for commanding an opening and closing mechanism of an electrical switchgear apparatus, in particular for command of a power circuit breaker.
The document DE 2,340,450 describes a latching device with detent balls for latching an electrical switch, comprising a latching bolt sliding in translation in a case and a control sub-assembly formed by a control rod with axial movement arranged perpendicularly to the axis of translation of the bolt and equipped with a support plate for two balls. In the latched position, a first of the two balls bears on one side on a flat end of the bolt and on the other side on the rod. The surface of the flat end of the bolt is parallel to the contact surface of the rod so that the bolt only transmits purely radial forces to the rod. These forces are taken up by the second ball located between the rod and the case. The end of the bolt further comprises in a bottom part a chamfer forming a ramp. To release the bolt, the rod simply has to be moved, so that the first ball rolls into contact with the rod on the one hand and with the flat end of the bolt on the other hand, until it is facing the ramp of the bolt. At this moment, the ball is ejected and releases the bolt. Such a device has a relatively good performance, but it is extremely sensitive to dimensional tolerances and to wear of the parts. The forces applied to the rod by the two balls are great and can leave an imprint in the rod. Moreover, if the diameter of the second ball does not correspond exactly to the distance between the rod and the case, the radial forces transmitted to the rod by the first ball in the latched position will not be fully transmitted to the second ball and will tend to deform the rod.
The document DE 1,131,304 describes a latching device of a catch of a high-voltage electrical switch, comprising a latching bolt sliding in a case and bearing on a row of four rollers. In the latched position, the four rollers are aligned in the axis of translation of the bolt, and the roller the farthest away from the bolt bears on a wall of the case. A push-button enables the intermediate rollers located in second and third position to be de-aligned, but these intermediate rollers are biased to the alignment position by return springs. So long as alignment of the four rollers is maintained, the force exerted by the bolt is transmitted in full from roller to roller up to the case. When the push-button is actuated, the two intermediate rollers are made to roll to their de-aligned position against the biasing force of the return springs. As soon as the alignment of the rollers has been broken, the bolt is released. The ability to keep the intermediate rollers in the alignment of the bolt depends on the calibration of the return springs. As soon as the intermediate rollers start to be de-aligned, a large part of the force exerted by the bolt is in fact transmitted to the return springs. As soon as the device is subjected to impacts or vibrations tending to de-align the rollers, the return springs are subjected to strong stresses due to the forces exerted by the bolt. If the sensitivity of the device to impacts is to be decreased, the stiffness of the return springs has to be increased, so that the force to be applied on the rod to de-align the device increases. The travel of the bolt is moreover limited.
The object of the invention is therefore to remedy the shortcomings of the state of the prior art so as to propose a ball actuator of great efficiency, requiring a very low operating energy to release a high mechanical energy.
Another object is to reduce the dimensions of the actuator for a given stored mechanical energy. Another object is to increase the travel of the movable means delivering the stored kinetic energy. Another object is to make the actuator mechanism relatively insensitive to dimensional variations due to manufacturing tolerances or wear. Another object is to make the actuator relatively insensitive to mechanical impacts and vibrations. Another object is to increase the speed of the actuator. In a more general manner, another object is finally to reduce the manufacturing cost of the actuator.
According to the invention, these objectives are achieved by means of an actuator comprising:
a case defining a geometric axis of translation;
a control rod movable in translation with respect to the case in a direction parallel to the geometric axis of translation between a latched control position and an unlatched control position, and comprising a rolling surface,
a striker movable in translation with respect to the case in a direction parallel to the geometric axis of translation between a loaded position and an unloaded position, and comprising a bearing collar,
a drive means of the striker operating in conjunction with the striker in such a way that when the striker is in its loaded position, the drive means of the striker bias the striker to return to the unloaded position,
a set of n detent balls, n being an integer greater than or equal to three, each detent ball being movable between a latched position and a cleared position, each detent ball in the latched position being pressing against said bearing collar of the striker, each detent ball having a center,
a set of n control balls, each control ball having a center,
the actuator being such that when the striker is in the loaded position and the rod is in the latched control position, the centers of the detent balls are located in a first geometric plane perpendicular to the geometric axis of translation, the centers of the control balls are located in a second geometric plane perpendicular to the geometric axis of translation, each control ball is bearing against the rolling surface of the rod and against two corresponding detent balls belonging to the set of detent balls and the center of each control ball is situated between the rod and a third geometric plane parallel to the geometric axis of translation and passing through the center of each of said two corresponding detent balls.
Placing a control ball between two detent balls enables a distribution of the forces to be achieved such that the forces applied by the control balls to the rod have a component perpendicular to the axis of translation of the rod which is lower than the component in a plane perpendicular to the axis of translation of the rod of the forces applied by the striker to the detent balls. In other words, part of the forces applied by the striker are not transmitted to the rod. The operating energy required for movement of the rod between its latched control position and its unlatched control position is therefore low. This enables the power, consumption and dimensions of the rod drive means to be reduced.
Furthermore, the movable mass formed by the balls is relatively small and movement thereof is of very small amplitude, on the one hand unlatching of the striker consecutive to movement of the rod is very fast, which ensures a particularly good response time, and on the other hand the potential energy stored in the spring is almost fully transmitted to the striker, which ensures a very good efficiency of the mechanism.
Moreover, movement of the rod is perpendicular to the first and second planes, so that the balls work by rolling on the rod, and not by sliding, resulting in minimal wear.
Preferably, the drive means of the striker comprise an energy storage spring operating in conjunction with the case and with the striker, in such a way that when the striker is in its loaded position, the energy storage spring is in a loaded state and biases the striker to return to the unloaded position. The energy required to drive the rod is very small for a high potential energy stored in the energy storage spring. The actuator achieved constitutes a functional unit not requiring large adjustments when installation thereof is performed.
Preferably, the energy storage spring is a helical spring coaxial with the geometric axis. The rod is arranged along the geometric axis of translation, the bearing collar of the striker forms a surface of revolution around the geometric axis of translation, the centers of the detent balls form n peaks of a polygon with n sides centered on the geometric axis of translation and the centers of the control balls form n peaks of a polygon with n sides centered on the geometric axis of translation. The control balls are thus automatically centered by the combined action of the detent balls, which makes the device relatively insensitive to the effects of dimensional dispersions and wear.
Preferably, the device comprises in addition a return means for returning the rod to the latched control position and a drive means for driving the rod to the unlatched control position. Due to the reduction of the latching forces obtained by means of the relative arrangement of the control balls and of the detent balls, the force that has to be exerted by the return means of the rod is relatively low, so that the drive means of the rod only has to supply a small amount of energy to counteract the action of the return means of the rod and to drive the rod to the unlatched position.
According to a preferred embodiment, a movable assembly made of ferromagnetic material slides in translation securedly with the rod. The drive means of the rod comprise an electromagnetic excitation winding to drive the movable assembly.
Advantageously, the movable assembly is housed in a cavity of the case. The winding is supported by the case. The chains of dimensions are then reduced. The reliability of the device is thereby improved. Furthermore, the assembly obtained is particularly compact.
Advantageously the movable assembly is formed by a part of the rod. The number of parts is therefore reduced.
According to one embodiment, the return means of the rod comprise a permanent magnet attracting the movable assembly. The permanent magnet alone is sufficient to keep the rod in the latched position and possibly to perform resetting of the rod either completely or in part. This enables the electrical consumption of the control actuator to be reduced considerably. Alternatively or cumulatively, the return means of the rod comprise a return spring.
According to one embodiment, the rod comprises an axial stop whereon the control balls bear when the striker is in the loaded position and the rod is in the latched control position, the first and second geometric planes being distinct, the second geometric plane being situated between the first geometric plane and the axial stop. With such an arrangement, the mechanism is polarized mechanically to the unlatched position since the resultant of the forces applied by the control balls on the rod comprises an axial component. Take-up of the play between the balls is even more efficient.
Preferably the rod, when moving from the latched control position to the unlatched control position, moves in an operating direction, the second geometric plane being offset from the first geometric plane in said operating direction. The resultant of the forces exerted by the control balls on the rod then has an axial component tending to drive the rod to its unlatched control position. The tripping movement is then very fast, and the power required to move the rod to the unlatched position is very low.
Alternatively, it is possible for the first and second planes to be one and the same. In this case, the forces transmitted to the rod are purely perpendicular to the geometric axis of translation.
Advantageously a movable auxiliary push-button drives the rod from the latched control position to the unlatched control position passing from a first position to a second position.
The push-button enables the mechanism to be actuated manually to check the operation of the actuator. It also enables tripping to be performed by a mechanism external to the device and designed to operate in parallel with the electromagnetic control actuator.
Advantageously, the control balls, the detent balls and at least a part of the rod are housed in a cavity confined by walls of the case and by the striker, said walls forming a guiding surface operating in conjunction with the striker so as to achieve dust-tightness when the striker moves between the loaded position and the unloaded position. Reliability of the mechanism is thus achieved with a great saving of means.